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> From: Michael Sperber <sperber@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
> Tom> SCHEME_FALSE, SCHEME_TRUE, SCHEME_NULL, and
> Tom> SCHEME_UNSPECIFIC should be functions, not constants:
> Why?
> Tom> [...] because, you never know, those constants might be
> Tom> heap allocated.
> That, AFAICS, doesn't mandate the above.
Perhaps it would be clearer if I said that those constants may be
_newly_ heap allocated.
It isn't GC-safe to return values which may be unprotected from GC.
If you were to use JNI-style allocated handles for everything then
those macros could be written as specified. I think the drawbacks to
that approach outweigh this and other minor syntactic advantages,
however.
Anyway, why is it important to write them that way? You can't use
them with == or !=. Doing it your way they're just "different" from
every other value in the system apparently because of a non-portable
bias towards assuming that they are implemented as immediate values.
-t